ABSTRACT
Invertebrates are particularly useful for analyzing the neural and molecular events underlying learning. The nervous systems of many invertebrates contain only several thousand cells (compared with the billions of cells in the vertebrate nervous system). Despite the small number of cells, an invertebrate ganglion can control a variety of different behaviors. A given behavior may therefore be mediated by 100 neurons or less, and this small size of the circuit makes complete description easier. Moreover, many neurons are relatively large and can be repeatedly identified as unique individuals, permitting one to examine the functional properties of an individual cell and to relate those properties to a specific behavior mediated by the cell. Changes in cellular properties that occur when a behavior is modified by learning can then be related to specific changes in behavior. Molecular and biophysical events underlying the changes in cellular properties can then be determined.
